She's at the age where she wants to act like a girl
She's reached the age where she wants to do girly things
She's at the age where she wants to be treated like a girl
「女の子"をしたい」＝ be girly / do girly things / act like a girl
「年頃」＝ the age
「女の子"をしたい年頃」＝ She's at the age where she wants to act like a girl / She's reached the age where she wants to do girly things / She's at the age where she wants to be treated like a girl
She's at the age where she wants to act like a girl.
「女の子をしたい年頃」と英語で言いたい場合、次のように表現できます。
・She's at the age where she wants to act like a girl. 「彼女はちょうど女の子らしく振る舞いたい年頃です。」
また、他の言い方も紹介します：
・She's at the stage where she wants to express her femininity. 「彼女は今、女性らしさを表現したい時期です。」
・She's at that age where she likes to do girly things. 「彼女はちょうど女の子らしいことをしたい年頃です。」
・She's in a phase where she enjoys being a typical girl. 「彼女は今、典型的な女の子であることを楽しむ時期です。」
イギリス 
アメリカ合衆国 
